Ok, dudette, here we go. This was too much fun, so it's rather long...

Adrian (Emperor Hadrian)
Alder (the tree, I think this is really cute with Rowan)
Alexas (from Shakespeare's Antony & Cleopatra)Altair (the star)
Arion (Greek mythology; cithara player and poet)Arun (Hindi name, it derives from Aruna who was the charioteer of the sun)
Arundel (a surname, I just think it's cute. means "little swallow")Aspen (the tree, maybe you don't want another tree name, I just couldn't resist. Aspens are so beautiful.)
Atys (a name of kings, also a young man who loved Cybele and was turned into a pine tree.)
Aylwin (from Barbara Pynn's No Fond Return of Love)
Bellerophon (Greek mythology; he killed the chimera)
Beltane (Pagan festival, not sure how you feel about that. I think it's beautiful and lush.)Briar (BriarRose and all that.)
Calidore (from The Faerie Queene; The Knight of Courtesy)Cambell (from The Faerie Queene; The Knights of Friendship)Celestine (historical, used by some popes.)Cyprian (a saint)Daron (a Welsh river, connected to places in Arthurian legends. Might also be a God or Goddess.)
Deronda (from GeorgeEliot's Daniel Deronda)Diarmaid (old Irish name, several kings and saints have born it)
Elfed (Welsh name for an old Brythonic kingdom in Yorkshire (also Alban Elfed, the Autumnal Equinox)Elon (Biblical, a judge. Means "oak".)Ember (I simply think this would look cute with Rowan. But maybe too wordy? And unisex, of course.)
Enlil (Chief God in the Sumerian Pantheon)
Eomer (from Tolkien's The Lord of the Rings)Eyre (surname, and CharlotteBronte's JaneEyre)
Finvarra (Irish folklore; High King of Daoine Sidhe)Florian (used by saints, and an emperor)
Florizel (from Shakespeare's The Winter's Tale)
Ganymede (Greek mythology; beautiful young man loved by Zeus)Garnet (gem stone, cute with Rowan)
Gwion (Welsh mythology; long story, but essentially he swallowed by Ceridwen and nine months later out came Taliesin.)
Herla (Germanic mythology; leader of the WildHunt)
Iamos/Iamus (Greek mythology; Evadne's son, abandoned and found on a bed of violets by snakes who fed him honey. "Boy of the violets".) Ilan (Hebrew, means "tree")
Isten (Hungarian pagan Chief God)Ivo (Old Germanic, means "yew")
Jarilo (Slavic God of spring, fertility, moon, vegetation)Julian (I like this for you; I know it's not obscure, but it was unisex back in the middle ages. Character in Iris Murdoch's The BlackPrince (a girl!))
Lanval (from awesome medieval CHICK poet Marie de France's poem "Lanval". Knight of KingArthur and lover of a fairy.)Leander (Hero & Leander)Leslie (it's not obscure, but it's cute. "garden"+"holly")
Lorien (Lord of the Rings! The master of dreams and visions. Also the elven forest!)
Loxias (Greek mythology; epithet of Apollo)
Lupin (a plant with gorgeous flowers, and it symbolises admiration!)
Mabon (Celtic mythology; one of the most important Gods, it means "Divine son")Marin ("of the sea". You wanted to honour someone sea related, right?)Marinell (The Faerie Queene; The Knight of the Sea)
Meirion ("of the sea"; born by Welsh kings)
Melion (a knight in a piece of medieval English romance (Breton Lai))Mitra/Mithra (Indo Iranian God, also Mithras; Greco-Roman God)Ninian (Celtic saint, probably an early obscure God turned into a saint)
Orchil (This is a girl name, so I'm sorry for throwing it in here. She's a SaxonEarthGoddess.)Orlando (Frankish military leader, and VirginiaWoolf's Orlando)
Perun (Slavic God of Thunder)
Polydore (Greek mythology; KingPriam of Troy's youngest son. Also a character in Shakespeare's Cymbeline)
Reasmay (unisex, but it's pretty and means "ray of liht"!)
Rosslyn (the Rosslyn Chapel in Roslin, Scotland)
Salerio (from Shakespeare's The Merchant of Venice)Salix (Latin for willow)Seaborn (surname... but it's so pretty!)
Seamay (another girl name, I apologise, but it's gorgeous so I couldn't help myself)Seraphim (the name of the highest level of celestial beings. Burning serpents or many winged creatures.)
Somerled (old Norse name)Valerian (a Roman emperor, some saints, and the herb!)Vasant (an attendant of the Hindu God of Love)
Vervain (herb of healing, it's magical and sacred)
Viorel (means "violet")Vivian (saints and used since medieval times)Yarrow (fantastic herb with mythological ties)

I will try and do some ideas that don't sound trendy "boy name on girl" but are boy/unisex names indeed and will be cute for a girl, I am sure they all have some culture connections as well.
I am third Garnet, I have such a crush on it. Also(sorry, not in ABC order):Marion(used to be boy's name;also an ancient city, Cyprus)Valentine(St Valentine and so on)Foma(how cool it will be to use Russian Thomas? Used to be Russian classic writers' favorite.)Asher (do you remember EdgarPoe's story? Love it.)Nikita(101% boy in Russia and Ukraine, you will never meet a girl Nikita there. Nikita is a folk character.Apollo (he was such a sex symbol, ha ha...But I see it on a girl very well, Polly can be a nickname)Basil(a lot of references but my favorite is a "Picture Of DorianGray" character)
Taras(not Tara with -s but an Ukrainian classic, highly popular there. NikolaiGogol's Taras Bulba comes to mind)Joachim(saint; also a character in Norwegian "The ChristmasMystery")Jude(The Beatles! Can be cute for a girl)Byron(besides poetic reference, it's such a cool unisex name)
Agam(Israeli unisex name, means "lake")
This was fun